In an internal combustion engine, particularly in a Diesel engine, an injection pump such as in-line type or distributor type is used for feeding fuel under pressure to a cylinder or cylinders of the engine. Generally, such injection pump includes a cam shaft connected to the driving shaft of the engine for rotation therewith, and one or more plunger means arranged to be driven by the rotating cam shaft for reciprocal motion to feed under pressure or inject fuel to the cylinder or cylinders of the engine.
It is conventionally known that in these injection pumps the cam shaft undergoes a change in torque between the injection stroke and the non-injection or return stroke of the plunger so that there occurs a torsional vibration in the cam shaft, resulting in variations in the angular velocity of the cam shaft. Such an injection pump is provided with a centrifugal governor which is usually arranged within the housing pump for varying the injection quantity of the injection pump to control the engine speed through displacement of the shifter which is movable in response to opening or closing motion, i.e., radially outward or inward pivoting of the flyweights pivotally mounted on the cam shaft of the injection pump. Under such arrangement, the cam shaft of the pump may sometimes be subject to torsional vibration, which in turn causes vibration of the flyweights and other governor component elements connected thereto including the shifter, links such as a tension lever and a floating lever, and control rack, thus resulting in the disadvantage that the governor fails to stably control the engine and the points of contact between the individual component elements undergo abrasion or wear.
In order to eliminate such disadvantage, it has conventionally been proposed to interpose a vibration absorbing material such as a rubber damper between the cam shaft of the pump and the flyweights. This measure is now generally employed. However, it requires a rather complicated construction. Further, since removal of the cam shaft from the pump is not so easy, there occur many problems in the manufacture, mounting and maintenance of such absorbing material, resulting in very low mass productivity and practicability. Furthermore, the frequency of torsional vibration of the rotating cam shaft may often be equal to the proper or natural vibration frequency of the rubber used as the damper. In such event, the two members resonate to provide a source of vibration, imparting a torsional vibration of larger amplitude to the flyweights.